I wouldn't think it's IB...Have you ever spotted with ovulation? What does your CM look like? (like over the past few days - is it egg white-ish, sticky, creamy etc). If you're only on CD17 I would think you're o'ing a couple days later or had some irritation (sex does that for me sometimes). But I'd also just whip out a stick (one of each!) for grins and giggles